If you die without making a Will (i.e. intestate – view the Intestacy flow chart here) your estate and guardianship of any minors will be handled by the state.
Which, even with the simplest of estates, might not be what you want. Someone would have to be appointed as your personal representative to administer your estate – either a family member or friend would have to put themselves forward to take on this role or the courts would appoint someone, which could end up being a professional able to charge your estate for their time and any costs incurred administering it.